Chendu College of Engineering & Technology the advantages of PMMC instruments ... Two wattmeter...
Transcript of Chendu College of Engineering & Technology the advantages of PMMC instruments ... Two wattmeter...
Page 1
Chendu College of Engineering & Technology (Approved by AICTE, New Delhi and Affiliated to Anna University)
Zamin Endathur, Madurantakam, Kancheepuram, District – 603311.
DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING
TWO MARK QUESTION WITH ANSWER
SUBJECT NAME: Measurements & Instrumentation YEAR/SEM: III/VI
SUBJECT CODE: EC2351 PREPARED BY: Mr.A.MOHAIYADEEN AP/ECE
UNIT-I
BASIC MEASUREMENT CONCEPTS
1. What is meant by measurement?
Measurement is an act or the result of comparison between the quantity and a predefined standard.
2. Mention the basic requirements of measurement.
· The standard used for comparison purpose must be accurately defined and should be commonly
accepted.
· The apparatus used and the method adopted must be provable.
3. What are the 2 methods for measurement?
· Direct method and
· Indirect method.
4. Explain the function of measurement system.
The measurement system consists of a transducing element which converts the quantity to be
measured in an analogous form. The analogous signal is then processed by some intermediate means and
is then fed to the end device which presents the results of the measurement.
5. Define Instrument.
Instrument is defined as a device for determining the value or magnitude of a quantity or variable.
6. List the types of instruments.
· The 3 types of instruments are
· Mechanical Instruments
· Electrical Instruments and
· Electronic Instruments.
7. Classify instruments based on their functions.
Indicating instruments, integrating instruments, Recording instruments
Page 2
8. Give the applications of measurement systems.
· The instruments and measurement systems are sued for
· Monitoring of processes and operations.
· Control of processes and operations.
· Experimental engineering analysis.
9. Define static characteristics?
Static characteristics are the set of rules or criteria that is defined for those instruments that
varies very slowly with time or remains a constant.
10.Define Dynamic characteristics?
Dynamic characteristics are the set of rules or criteria that is defined for those instruments
that varies very rapidly with time.
11.What are the various Dynamic characteristics?
Various Dynamic characteristics are
Fiedality
Speed of Response
Time Delay
Lag
Dynamic error
12. What are the various Static characteristics?
Various Static characteristics are
Accuracy
Precision Error
Threshold Bias
Linearity
Stability
Reproducibility
Hysterisis Range
Dead Space
Page 3
Sensitivity.
13. What are the various units of measurements?
Units are the fundamental quantities of physics; Various units of measurements are
Fundamental Units e.g.: Length (m), Mass (kg), and time (S) Supplementary Derived Units
14. Name the different essential torques in indicating instruments.
Deflecting torque
Controlling torque
Damping torque
15. Name the types of instruments used for making voltmeter and ammeter.
PMMC type, Moving iron type, Dynamometer type, Hot wire type, Electrostatic type,
Induction type.
16. State the advantages of PMMC instruments
Uniform scale.
No hysterisis loss Very
accurate High effuiciency.
17. State the disadvantages of PMMC instruments
Cannot be used for ac m/s
Some errors are caused by temperature variations.
18. State the applications of PMMC instruments m/s of dc voltage and current
Used in dc galvanometer.
19. How the range of instrument can be extended in PMMC instruments.
In ammeter by connecting a shunt resister
In voltmeter by connecting a series resister.
20. State the advantages of Dynamometer type instruments
Can be used for both dc and ac m/s.
Free from hysterisis and eddy current errors.
Page 4
21. State the advantages of Moving iron type instruments
Less expensive
Can be used for both dc and ac
Reasonably accurate.
22. State the advantages of Hot wire type instruments
Can be used for both dc and ac
Unaffected by stray magnetic fields
Readings are independent of frequency and waveform
23. What are the various types of Bridges?
There are basically two types of bridges
A.C
Bridge
D.C
Bridge
Kelvin’s
Bridge
Maxwell’s
Bridge
Hay’s
Bridge
Schering’
s
Bridge
Wein
Bridge Andreson’s
Bridge
Wheatstone
sBridge
5
24. Name any one Bridge that is used to measure the frequency?
Wein Bridge
UNIT-II
BASIC ELECTRONIC MEASUREMENTS
1. What are the constructional parts of wattmeter?
Fixed coil
Moving Coil
Current limiting resister
Helical spring
Spindle attached with pointer
Graduated scale
2. Write down the deflecting torque equation in dynamometer type wattmeter.
Td á VI CosÖ
3. What is the principle of CRO
Cathode ray oscilloscope works on the the principle of deflection of the electron beam
in the horizontal and vertical directions and creates the trace on the fluorescent screen.
4. Name the errors caused during measurement Error
due to pressure coil inductance Error due to pressure coil capacitance Error due to methods of
connection Error due to stray magnetic fields Error due to eddy current.
5. What is meant by special Oscilloscope?
The oscilloscope which is not only meant for viewing the waveform , but also used to
perform some special functions such as storage of information, retrival of waveform, stability
etc..
6. What is meant by special Oscilloscope?
Various types of special oscilloscopes are
• D S O
• D e l a y e d time base oscilloscope
• D u a l trace oscilloscope
• D u a l Beam oscilloscope
• S a m p l i n g oscilloscope
7. Name the methods used for power measurement in three phase circuits.
6
(i) Single wattmeter method
(ii) Two wattmeter method
(iii) Three wattmeter method.
8. What is meant by Phosphor burning?
The process in which the trace of the waveform is obtained on the phosphor screen, and
when the trace is present for long time, the heat generated is capable of destroying the phosphor
screen, which is known as phosphor burning.
9. How is phosphor burning avoided?
The destructive method phosphor burning is avoided by coating the fluorescent screen
with a layer of Willemite, which is the composition of zinc and Mno2
10. What is meant by fluorescence?
The ability of the material to emit energy is known as fluorescence. When phosphor exhibits
the fluorescence property, it is known as phosphorescence.
11. What is meant by Q-factor?
Q-factor is known as the quality factor. It is used to measure the quality factor of
the coils such as inductors, Capacitors etc..
12. What is meant by Q-meter?
Q-meter is generally used to measure the Q-factor of the coil.
13. Name the constructional parts of induction type energy meter.
Current coil with series magnet Voltage coil with
shunt magnet all disc
Braking magnet
Registering mechanism.
14. What is a True RMS METER?
The true RMS meter is used to determine the rrot mean square value of the current and
voltage.
15. What are the various types of storage oscilloscopes?
The various types of storage oscilloscopes are
• A n a l o g storage oscilloscope
Mesh storage oscilloscope
Bistable phosphor storage oscilloscope
• D i g i t a l storage oscilloscope
7
16. What is the DSO?
DSO is known as digital storage oscilloscope, it is used for storing the waveform in a
digital form. It consits of a sample and hold circuit, control logic and an A/D converter the
waveform can be stored in a buffer amplifier.
17. What is meant by special Oscilloscope?
The oscilloscope which is not only meant for viewing the waveform , but also used to
perform some special functions such as storage of information, retrival of waveform, stability
etc..
18. What is the purpose of braking mechanism?
It provides necessary braking torque.
19. What are the applications of CRO?
CRO is used in
Medical field
Waveform analysis
Study of time period and amplitude of the waveform
Military applications.
20. What are the various methods of RF power measurement?
The various methods used in RF power measurements are
• C a l o r i e m e t e r power meter
• Power measurement at high frequencies by
• B o l o m e t e r power meter
UNIT –III
SIGNAL GENERATORS AND ANALYZERS
1. What is Function Generator? The function generator is the device which is capable of producing several functions based on the
trigger input given.
2. Name the potentiometer material used.
German silver
Manganin wire
3. Define standardization.
8
It is the process by which adjusting the current flows through the
potentiometer coil to make the voltage across the std cell is equal.
4. State the applications of potentiometer.
Used for m/s of unknown emf Used for ammeter calibration Used for Voltmeter calibration
Used for wattmeter calibration
5. What are the various types of signal generators?
• S w e e p signal generator
• A u d i o frequency signal generator
• R F signal generators
6. What are the types of frequency synthesizer?
There are two methods of frequency synthesis, they are
Direct frequency synthesis
In-direct frequency synthesis
7. What is meant by harmonic distortion?
Any unwanted harmonics that are present along with the needful information is known as
Harmonic Distortion.
8. How the phase angle is measured in polar type potentiometers.
It is measured from the position of phase shifter.
9. Name some ac potentiometers.
Drysdale Tinsley potentiometer
Gall Tinsley potentiometer
10. State the advantages of ac potentiometers.
Can be used for m/s of both magnitude and phase angle
Can be used for m/s of inductance of the coil. It is used in m/s of errors in CTS
11. State the applications of ac potentiometers.
M/s of self inductance.
Ammeter calibration
Voltmeter calibration
Wattmeter calibration.
12. What are Detectors?
Detectors are used in an attempt to adequately map the correct signal power to the
appropriate frequency point on the display. There are in general three types of detectors:
sample, peak, and average
9
• Sample detection – sample detection simply uses the midpoint of a given interval as
the display point value. While this method does represent random noise well, it does not
always capture all sinusoidal signals.
• Peak detection – peak detection uses the maximum measured point within a given
interval as the display point value. This insures that the maximum sinusoid is measured
within the interval; however, smaller sinusoids within the interval may not be measured.
Also, peak detection does not give a good representation of random noise.
• Average detection – average detection uses all of the data points within the interval to
consider the display point value. This is done by power (rms) averaging, voltage
averaging, or log-power averaging.
13. State the disadvantage of instrument transformers.
Cannot be used for dc measurements.
14. What are the constructional parts of current transformer?
Primary winding
Secondary winding
Magnetic core.
15. Name the errors caused in current transformer.
Ratio error
Phase angle error
16. What is meant by Resolution Bandwidth?
As discussed in the operation section, the resolution bandwidth filter or RBW filter
is the bandpass filter in the IF path. Adjusting the bandwidth of this filter allows for the
discrimination of signals with closely spaced frequency components, while also changing the
measured noise floor. Decreasing the bandwidth of RBW filter decreases the measured noise
floor and vice-versa. This is due to higher RBW filters passing more frequency components
through to the envelope detector than lower bandwidth RBW filters, therefore a higher
RBW causes a higher measured noise floor.
17. What is meant by Wave analyzer?
Wave analyzer helps to evaluate the characteristics of wave such as frequency,
amplitude and Phase angle.
18. What is a Spectrum Analyzer?
Spectrum analyzer measures the magnitude of an input signal versus frequency within the
full frequency range of the instrument. The primary use is to measure the power of the
10
spectrum of known and unknown signals. The input signal a spectrum analyzer measures is
electrical, however, spectral compositions of other signals, such as acoustic pressure waves and
optical light waves, can be considered through the use of an appropriate transducer
19. What are the types of Spectrum Analyzer?
Spectrum analyzer types are dictated by the methods used to obtain the spectrum of
a signal. There are swept-tuned and FFT based spectrum analyzers:
• A swept-tuned spectrum analyzer uses a superheterodyne receiver to down- convert a
portion of the input signal spectrum (using a voltage-controlled oscillator and a mixer) to
the center frequency of a band-pass filter. With a superheterodyne architecture, the
voltage-controlled oscillator is swept through a range of frequencies, enabling the
consideration of the full frequency range of the instrument.
• A FFT spectrum analyzer computes the discrete Fourier transform (DFT), a
mathematical process that transforms a waveform into the components of its frequency
spectrum, of the input signal. Some spectrum analyzers, such as real-time spectrum
analyzers, use a hybrid technique where the incoming signal is first down-converted to a
lower frequency using superheterodyne techniques and then analyzed using fast fourier
transformation (FFT) techniques.
20. What is meant by center frequency?
In a typical spectrum analyzer there are options to set the start, stop, and center
frequency. The frequency between the stop and start frequencies on a spectrum analyzer display
is known as the center frequency. This is the frequency that is in the middle of the display’s
frequency axis. Span specifies the range between the start and stop frequencies. These two
parameters allow for adjustment of the display within the frequency range of the instrument to
enhance visibility of
the spectrum measured.
1. What is a Voltmeter?
UNIT-IV
DIGITAL INSTRUMENTS
11
A voltmeter is an instrument used for measuring electrical potential difference between two points in an
electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the
circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter.
2. What is a Digital Voltmeter?
Digital voltmeters (DVMs) are usually designed around a special type of analog-to-digital
converter called an integrating converter. Voltmeter accuracy is affected by many factors, including
temperature and supply voltage variations. To ensure that a digital voltmeter's reading is within the
manufacturer's specified tolerances, they should be periodically calibrated against a voltage standard
such as the Weston cell.
3. What is a multimeter?
A multimeter or a multitester, also known as a VOM (Volt-Ohm meter), is an electronic
measuring instrument that combines several measurement functions in one unit. A typical multimeter
may include features such as the ability to measure voltage, current and resistance. Multimeters may
use analog or digital circuits.
4. Where high resistance measurement is required?
Insulation resistance of cables High
resistance circuit elements Volume resistivity
of a material Surface resistivity.
6. What is the function of a Frequency Counter?
A frequency counter is an electronic instrument, or component of one, that is used for
measuring frequency. Frequency is defined as the number of events of a particular sort occurring in a set
period of time. Frequency counters usually measure the number of oscillations or pulses per second in a
repetitive electronic signal. Such an instrument is sometimes referred to as a cymometer, particularly one
of Chinese manufacture.
7. What is extension of frequency range?
Frequency extension of signal is defined as the deliberate process of expanding the frequency
range (bandwidth) of a signal in which it contains an appreciable and useful content, and/or the
frequency range in which its effects are such. Its significant advancement in recent years has led to the
technology being adopted commercially in several areas including psychacoustic bass enhancement of
small loudspeakers and the high frequency enhancement of coded speech and audio.
8. What is Automation in digital instruments?
12
It is used to fabricate a wide range of instruments and equipment for instrumentation, process
controls, automation and condition monitoring applications.
9. Define megger.
The megger is an instrument used for the measurement of high resistance and insulation
resistance.
10. What are the technical specifications of computer controlled test systems?
Technical Specifications
• Maximum load of 10N.m
• Intelligent Torque Loadcell capacities: 0.3N.m, 1.5N.m, 3N.m, 6N.m,
10N.m (2.7lbf.in, 13lbf.in, 26lbf.in, 52lbf.in, 90lbf.in)
• Maximum sample height of 448mm (17.6") *
• Width between columns 280mm (11")
• Capacity of upper mounting table from 10 to 78mm (0.39 - 3.07")
• Capacity of lower mounting table from 10 to 190mm (0.39 - 7.5")
• Load accuracy is ±0.5% of full scale
• Load resolution is 1:6500
• Speed range of 0.1 - 20 revs/min (clockwise and counter-clockwise)
• Maximum displacement of 2440 revs
• 5kg top loading capability
• Weight 19.5kg (43lb)
11. What is the range of low resistance?
Resistance of about 1 ohm and under are included in this class.
12. What is the range of medium resistance?
Resistance of 100 kilo ohms and above are usually termed as high resistance.
13. What ranges of resistance can be measured by using doctor ohmmeter.
0 to 500 micro ohms
0 to 5 milli ohms
0 to 50 milli ohms
0 to 500 milli ohms
0 to 5 ohms.
14. How resistance is measured in direct deflection method.
The deflection of galvanometer connected in series with the resistance to be measured gives a
measure of the insulation resistance.
13
15. Classify the cables according to their sheathing.
Armoured cables
Unarmoured cables.
16. What is meant by automatic Zeroing?
Earth lead Line lead
Guard lead.
17. How resistance is measured by using ohm meter method.
Series ohm meter method
Shunt ohm meter method.
18. Why Is LabVIEW Ideal for Creating Virtual Instruments?
LabVIEW is an integral part of virtual instrumentation because it provides an easy-to-use
application development environment designed specifically with the needs of engineers and scientists in
mind. LabVIEW offers powerful features that make is easy to connect to a wide variety of hardware and
other software.
19. What are the views in VI?
• Front panel and
• Grid panel
20. What is meant by Virtual instrumentation?
Virtual instrumentation is a method of creating a Real time Environment in a virtual platform by
Using software.
UNIT-V
ACQUISITION SYSTEMS AND FIBER OPTIC MEASUREMENTS
1. What is DAQ?
DAQ is known as Data Acquisition system, it is meant for collecting the data, organizing the
data, processing the data and storing the results.
2. What is meant by multiplexing?
Multiplexing is the the process of combining several input signals. Many inputs are
multiplexed and the result is produced based on the select signal.
3. What is IEEE 488 bus?
14
IEEE 488 bus is formerly known as Hewlett Packard interface Bus. And later it was given
IEEE standard and was known as IEEE 488 bus. It is used to interface the digital multimeters,
digital voltmeters and so in.
4. What are the various devices in IEEE 488 Bus?
Various devices in IEEE 488 Bus are
Talkers. Listeners and
Controllers.
5. Name the bridge circuits used for the m/s of mutual inductance.
The Heaviside Campbell bridge
The Campbell bridge.
6. Which type of detector is used in ac bridges?
Vibration galvanometers are used.
7. Name the ac sources used in ac bridges.
AC supply with step-down transformer
Motor driven alternator
Audio frequency and radio frequency oscillator.
8. In which cases audio frequency oscillators are used as ac source.
For high frequency ac requirement audio frequency oscillators are used.
9. Name the sources of errors in ac bridge m/s.
Errors due to stray magnetic fields
Leakage errors Eddy current
errors Residual errors
Frequency and waveform errors.
10. State the advantages of Maxwell-wein bridge.
The balance equation is independent of frequency and therefore more accurate.
11. State the disadvantage of Maxwell-wein bridge.
This method needs a std variable capacitor. Variable Capacitor is costliest.
12. State the disadvantages of Hay’s bridge.
The balance equation is dependent of frequency and therefore any changes in frequency will
affect the measurements.
13. What is Total internal reflection?
15
When the light ray travels from the optically rarer medium to the optically denser medium the ray
gets refracted and some of the rays gets reflected, when the angle of incidence is increased, the angle of
refracted also get increased and at a particular point all the rays get reflected and no refraction occurs.
This is known as Total Internal reflection
14. What are the various methods of fiber optic power measurement?
Various methods of fiber optic power measurement are Bolometer power meter
Power meter
Auto ranging power meter
15. What is meant by inductometer?
The std variable mutual inductance meter is called as inductometer.
16. Define Q-factor of the coil.
It is the ratio between powers stored in the coil to the power dissipated in the coil.
17. Name the components of iron loss.
Eddy current loss
Hysterisis loss.
18. Name the faults that occur in cables.
Break down of cable insulation
Short circuit fault
Open conductor fault.
19. Name the loop test methods used in location of fault in fiber.
Murray loop test
Varley loop test.
20. What is OTDR?
OTDR is known as Optical Time Domain Reflectometer. It is used for the measurement of the
fiber optic system loss. In this method the directional coupler is used so that losses are reduced.